Questions and Answers
During the log phase, what is characteristic of the microbial population?
What is the primary reason for the slowing of growth in the exponential phase?
In the stationary phase, what is the balance between?
What is a common reason for aerobic microorganisms to enter the stationary phase?
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Why do cells beneath the surface of a batch culture stop growing?
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What can cause the accumulation of toxic waste products?
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In what type of environment do bacteria enter the stationary phase due to starvation?
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What is the significance of the log phase in microbial growth?
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What occurs during the death phase of microbial growth?
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How is the viability of a bacterial cell determined?
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What is the definition of death in the context of microbial growth?
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What is the purpose of a continuous culture system?
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In a batch culture system, what happens to the exponential growth phase?
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What is the primary reason for the lag phase in microbial growth?
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What is the significance of generation time in microbial growth?
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What happens to the cell mass during the lag phase?
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Why is the lag phase longer when the inoculum is from an old culture?
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What is the definition of generation time?
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What happens to the microorganism population during the exponential phase?
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Why is the lag phase shorter when the inoculum is from a fresh exponential phase culture?
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What is the primary characteristic of the exponential phase?
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What is a vital period prior to cell division?
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What is the primary advantage of continuous culture systems in microbiology research?
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Which type of bacteria lacks superoxide dismutase and catalase, making oxygen lethal to them?
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What is the term for bacteria that require higher amounts of CO2 for their growth?
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What is the optimum temperature for most pathogenic bacteria?
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Which factor affects bacterial growth by providing energy from sunlight?
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What is the term for bacteria that use chemical sources as their source of energy?
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Study Notes
Bacterial Growth
- Microbial growth is defined as an increase in cellular constituents resulting in an increase in microorganism size, population number, or both.
Generation Time
- Generation time is the time required for a bacterium to give rise to two daughter cells under optimum conditions.
- It varies with the species of microorganism and environmental conditions, ranging from less than 10 minutes to several days.
Bacterial Growth Curve
Lag Phase
- When microorganisms are inoculated into fresh culture medium, they will not reproduce immediately, and this period is called the lag phase.
- During the lag phase, bacterial cells synthesize new components, including ATP molecules, essential cofactors, and ribosomes, preparing for cell division.
- The lag phase varies in length depending on the surrounding conditions, such as the age of the inoculum and the chemical difference between the original and new medium.
Exponential (Log) Phase
- Microorganisms start to replicate their number in logarithmic order at a maximal rate.
- During the log phase, microorganisms grow under constant conditions, including nutrient and division rate, causing a uniform and identical new cell production at regular intervals.
- The population is most uniform in chemical and physiological characteristics, making exponential phase cells suitable for biochemical and physiological studies.
Stationary Phase
- The total number of viable microorganisms remains constant, resulting from a balance between cell division and cell death or the population ceasing to divide while remaining metabolically active.
- Microbial populations enter the stationary phase due to nutrient limitation, oxygen availability, and the accumulation of toxic waste products.
Death Phase
- A decline in the number of viable cells results from unsuitable conditions, and the death of microbial populations may be logarithmic like their growth during the log phase.
- Death is defined as the irreversible loss of the ability to reproduce.
Measurement of Microbial Growth
- Measurement of microbial growth can be determined by:
- Measurement of cell numbers
- Measurement of cell mass
Types of Culture Systems
Batch Cultures or Closed System
- Inoculum supplies are not renewed, nor are wastes removed, leading to exponential growth lasting only for a few generations before reaching the stationary phase.
Continuous Culture System (Open System)
- Microorganisms grow in a system with constant environmental conditions maintained through continual provision of nutrients and removal of wastes.
- This system allows for a microbial population to be maintained in the exponential growth phase and at a constant biomass concentration for extended periods.
Factors Affecting Bacterial Growth
- Oxygen: Bacteria can be classified into aerobic and anaerobic bacteria based on their oxygen requirements.
- Carbon dioxide: Capnophilic bacteria require higher amounts of CO2 for their growth.
- Light: Bacteria may be classified as phototrophs (from sunlight) or chemotrophs (from chemical sources) depending on their energy source.
- Temperature: The optimum temperature for most pathogenic bacteria is 37°C, and growth can be grouped based on temperature range.
- PH: Affects bacterial growth, with different bacteria having optimal pH ranges.
- Osmotic pressure: Also affects bacterial growth, with some bacteria being more resistant to osmotic changes than others.
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Description
Learn about the basics of microbial growth, generation time, and the different phases of bacterial growth curves. Understand how bacteria multiply and respond to environmental conditions.
